Cooler for gaseous suspension of a granulated solid



Sept. 14-, 1954 M E 2,689,112

COOLER FOR GASEOUS SUSPENSION OF A GRANULATED SOLID Filed Aug. 30. 1949F/GZ.

INVENTOR. F. E. GILMORE ATTORNE VS Patented Sept. 14, 1954 COOLER FORGASEOUS SUSPENSION OF :A I .GRANULATED S OLID of Delaware AppIicationAugust 3 0, 1949, Serial No. 113,036

This invention relates to an improvement in'a process, commonly-=termeda *hypersorptionprocess, whereintwo or more components oi a mixture areseparated byselective adsorption on an "adsorptive medium. in one ofitsaspec'ts this invention relates 'to a method for cooling a hot,freshly-stripped adsorptive =medium employed in a hypersorption process.1 In still another of its aspects this invention relates to a novelprocess for cooling a hot adsorptive medium wherein the said'medium issuspended in an entrainment gas and passed upwardly through a coolingzone. In a still further aspect this invention relates toa novel heat 7exchange; apparatus particularly adapted to cool a gaseous suspension ofahot adsorptive medium.

"In the prior 'art, several processes are known forseparatingone or morecomponents from a mixture thereof by selective adsorption onto a solidadsorp'tive mediumone SU'Ch processpis commonly termed a hyper-sorptionprocess. This process comprises introducing a feed gas comprising two ormore components, which are to be separated, into'a slowly moving bed ofsolid granular aadsorptive medium, such as activated H carbon, which iscontained in an elongated vertical hypersorption vessel and which 'isdesigned to adsorb; the heavier components of the mixture. Theadsorptive medium containing the adsorbed components is then contactedin a rectifying zone with a counterwurrent reflux of bottoms product'from the-process which contact serves to displace from the adsorptivemedium any of the undesired lighter'components originally adsorbed fromthe feed along-with the desired heavier components. The adsorptivemedium thus satu rated with the desired heavier components or bottoms'product next ,jpasses through astripping zone which usually comprises avertical tube bundle situated inside or thefhypersorpti'on vessel andheated externaily, say, by condensing 'Dowtherm vapors. Additionalstripping of the adsorbed components is accomplished by steam which isintroduced into the moving bed-of adsorbent below the Dowtherm heatingsection and which passesupwardly through the Dowthermtube bundlecounter-currently to the adsorptive mediumbeing stripped. The steam anddesorbed bottoms product or make gas are disengaged from the mov'ingbedat a point r above the stripping *zone and just below the rectifyingzone. The hot stripped aolsorptive medium leaving the Dqwtherm heaterpasses through a specially designed feed mechanism which-provides-apositive control of the adsorp- 2 tive medium flow rate and whichdistributes the medium evenly over the cross section ofthefhypersorption vessel. From this mechanism, the adsorptive mediumdrops into a sealing leg which restricts the flow of steam downwardlyfrom the stripping section. A gas lift system transports the adsorptivemediumlupwardly to the top of the hypersorber vessel where the flow isreversed by an impactless separation which reduces attrition to aminimum. The separated adsorpt'ive medium flows by gravity into a hopperat the top of the 'hypersorber wherein an operating ievel of thead'sorptive' medium is maintained. The medium then iiows downwardly bygravity into a vertically placed tubular heat-exchanger wherein themedium is cooled to a temperature satisfactory for further adsorptionin'the succeeding adsorption 'zon'e'. This completes one cycle of theadsorpt'ive 'med-i'um through the process. A typical hypersorptionsystem and adjunct equipment is described by 'Bland in PetroleumProcessing, pages 635-638, July, 'l'9i8. In the typical hypersorptionprocess, the cooling, adsorbing, rectifying and heating zones are allarranged in a single vertical vessel in the order named with the coolingzone being placed at the top of the vessel and the heating zone at thebottom. The usual cooling zone is comprised of a bundle of tubesarrangedwithinfthe hypersorption vessel in such a manner that the adsorbent to be cooled flows downwardly by gravity through the tubes whilethe cooling medium flows around the outside of the tubes and inside .a'shell formed by the walls of the hyper: scrption vessel. Such a systemis not conducive to eificient heat exchange between the adsorbent andthe cooling medium due to the low rate of how of adsorbent through thetubes. Consequently the length of the heat exchange tubes must berelatively long in order to provide sumc'ient cooling for the adsorptivemedium and as a result, the height of. the 'hypersorptiontower isunavoidably great. Another disadvantage in such a cooling system isoftenexperienced when ever stripping steam injected into the movingadsorbent below the Dowtherm heater escapes into the gas lift system dueto loss of level of adsorbent in the sealing leg. The steam' escape ingthrough the sealing leg travels upward with the adsorbent to the top ofthe hyp-ersorption vessel and into the cooling zone. There it condenseson the adsorbent particles and eiiectively plugs up the .tubes oftheadsorbent cooler. .The entire system mustthen be shut down and theclogged tubes cleaned of the wet adsorbent.

Further disadvantages in this system are found in the fact that the heatexchange equipment is in an elevated position, often as much as 160 feetabove the ground where it is difficult to control, clean or repair.Likewise due to its height above the ground, the coolant employed mustbe pumped to a high elevation in order to circulate through the heatexchanger. Such a procedure is wasteful of pumping energy. Also, theadsorbent must be elevated to an even higher elevation in order to flowthrough the heat exchanger and hence this results in excessive powercosts.

According to this invention, it has been found that the efficiency of ahypersorption process, wherein two or more components of a mixture areseparated by selective adsorption onto an adsorptive medium, can beincreased by cooling the freshly stripped hot adsorbent while it issuspended in an upwardly flowing gas stream. Still according to thisinvention, it has been found that the efficiency of a hypersorptionprocess can be increased by cooling the hot freshly stripped adsorptivemedium While it is being conveyed from the bottom of a hypersorptionvessel to the top thereof whereby the uppermost cooling zone in aconventional hypersorption system can be eliminated with a resultantdecrease in height to which the adsorbent must be elevated and to whichthe cooling medium must likewise be elevated and whereby the presence ofsteam in the cooling zone will not result in a clogging of said zonewith wet adsorptive medium. Still further according to this invention, anovel type of heat exchanger has been invented which is especiallyadapted to rapidly cool a granular solid medium suspended in a gaseouscarrier and which is further adapted to prevent clogging thereof withany of said medium which may separate from said carrier.

According to this invention the cooling zone at the top of aconventional hypersorption unit is dispensed with and the hot freshlystripped adsorptive medium is suspended in a gaseous carrier and passedthrough a novel heat exchanger especially adapted to cool a gaseoussuspension of a solid granular medium. As a result, the hypersorptionvessel comprises only 3 zones, namely, the adsorption, rectifying andstripping zones, thereby effectively reducing the height of said vessel.As stated, the hot, freshly regenerated adsorptive medium leaving thebottom-most zone of the hypersorption vessel is suspended in a gaseouscarrier and passed through a heat exchanger wherein it is cooled as itis transported upwardly to the uppermost (adsorption) zone of thehypersorption vessel. It has been found that when employing this featureof the invention the height of the hypersorption vessel is decreasedwith a resultant decrease in the power consumed in elevating theadsorptive medium and the cooling medium to the top of the hypersorptionvessel. of even more importance, however, the employment of the processof this invention results in a marked increase in the rate of heatexchange between the hot adsorptive medium and the cooling. mediumflowing counter-currently in the cooling zone due to the rapid rate offlow of the adsorptive medium through the heat exchange equipment. Astill further advantage flowing from the use of this system is that anysteam which may be present in the gaseous carrier will not cause aclogging of the cooling zone by the adsorptive medium. Especiallyadapted heat exchangers are employed in this process whereby the coolingof the adsorbent is effectively accomplished without undue attrition ofthe adsorbent particles and without any substantial settling of theadsorbent from the gaseous carrier.

In order to more fully understand the invention, it will be describedwith special reference to the attached drawings wherein Figure 1represents a schematic flow diagram of the process with particularreference to the cooling zone thereof. Figure 2 represents a novel typeof heat exchanger especially adapted to be employed in the process ofthis invention. Figure 3 represents an enlarged view of the conduitemployed in the heat exchanger of Figure 2. Figure 4 is across-sectional view taken on the line 4-4 as shown in Figure 3. Figure5 is another type of heat exchanger particularly adapted to be used inthe process of this invention. Figure 6 is a cross-sectional view takenon line 6-6 in Figure 5. In Figure 1, a slowly moving bed of adsorptivemedium in hypersorption vessel I flows downwardly by gravity throughadsorption zone 2, rectifying zone 3, stripping zone 4, heating zone 5,flow control zone In, and hopper II, in the order named. The feedstockwhich comprises a mixture of two or more components is introduced intoadsorption zone 2 through line 6 and it flows upwardly through theadsorption zone 2 wherein heavier selected components of the feedstockare adsorbed in the downward flowing adsorptive medium and the lighterunadsorbed components leave the vessel through line 1. The adsorptivemedium containing substantially all of the heavier components as well asunavoidably adsorbed minor portions of undesired light components flowsdownwardly from zone 2 into rectifying zone 3 wherein it iscounter-currently contacted with vaporous reflux derived from strippingzone 4. This reflux is adsorbed on the adsorptive medium therebydisplacing the undesired light components therefrom. The displaced lightcomponents then flow upwardly through zone 2 and out of the vesselthrough line 1. The adsorptive medium containing only the desired heavycomponents flows downwardly from zone 3 to stripping zone 4 and heatingzone 5 wherein ,it is heated to a temperature sufficiently high to stripit of substantially all of the adsorbed materials. These desorbed heavycomponents are withdrawn from the hypersorption vessel through line 8.

Heating zone 5 comprises a tubular heat exchanger disposed in the lowerportion of vessel I as shown. Dowtherm vapors, steam, or any othersuitable medium may be employed therein. Stripping steam is introducedinto the vessel through line 9 immediately below the heating zone 5.This steam aids in stripping the adsorptive medium. The stripping steampasses upwardly through vessel I along with the desorbed components andleaves the vessel through line 8. dium flows through a control mechanismIn which serves to regulate the flow of adsorbent through vessel I, andto effect a uniform crosssectional flow therethrough. After the hotadsorptive medium passes through hopper l I, it

flows into line [2 wherein it is picked up by a gaseous carrier which isinjected into line I2 through line l3. The gaseous carrier is usuallycomprised of overhead gases from line I and is propelled through line I3by blower l4. The gaseous suspension of hot adsorptive material nextpasses upwardly through heat exchanger IS The hot, freshly strippedadsorptive me-' 5 pdz enoet hr neh.line. Wcbflgk to the-to ofHWBIWPPISQFPHQH.FESSBI hus... mp tine a cycle 5.11 Pro e s. W hasp cieefe en e o he o ling syst m a she in-Eigurel; the suspensionofihotadsorbent ie passed upwardly through .a cooling conduit 11 s tedina vessel w Asatisfactorycoolant. sue as water or-othermedium,isintroducedinto es el 9. s n whe n-i fl w dow wet l nez ou. torur ento h a eo s u fl w n hrpusl p duit The, o a K rpmvessel IB -through linemend-flow contr Z I 'andi is discharged into; vessel 22 wherein flashsteamis removedthrough line 23 and s n t; ne hese h ine A. e. e fistructureofcooling conduit l l ismore fully decri edzheli w" Addi onal lr a b provided;bysurrounding.line :I GtWith jacket wherehythetentrainedadsorbent. is additionally cooled as, it is transported upwardly to thetop or thypersorption vessell, A coolant, which can be from the samesource as that employed. in vessel 1 llisintroduced into jacket25throughline 25., and. removed. therefrom through. line. 2 1.

he em e of: his-i n io cache em o toseparate amixtureof materialshavingdiffer.- ent ,adsorptiye. properties, Hence it can be used to separateethane andfethylene. from methane, propane, from. ethane nitrogen. from.methane, hydrogen chloride fromhydrocarbons; etc. The adsorptive mediumemployed is usually an activetted v charcoal such. as apricot pit orcoconut charcoal, Qther. media also be used, including activated.silica, activated alumina or activated carbon.' The particle size of thead.- sorptive medium can range from'about. 12 to ahout lt me 2 i e y eatee z b crating. temperatureot the. hypersorption process will; varywith. the. type or mixture being sep arat ed For example, lowertemperatures can be employedwhen. separating ethane from methane thanwhen. separating butane. from hutylene. In general. the temperature inthe adsorption zone will usually range from. about 100:. to about L5.0 EThe temperatures. in the. stripping zone. will range from about 35.0 toabout 7.00? but. they can be. even higher in order to desorb minor,portions of heavymaterials such as tarsf'polym'ers, etc., which enterwith; the. feedstock. The pres sure employed in the process. willlikewise vary with the material being treated but it can'usua le 1y.range from about atmospheric to about 3 00 pounds per square inch.

The velocity ofthe. feed flowing upwardly th h ads n c o 2 h uld b quitelow order that the adsorptive medium'therein will he efiectivelycontacted with the feed with a re. ui in e it sm e flr i n f' h t'sirponents of the mixed teed. For. example, vapor tie in th ran e of bou toP f a l from about, to L ieet per. second he satisfac Vapor velocitiesthe other zones con.- tained in the hy firsorption vessel arenot'critical. The velocity of the gaseous. suspending agenten-f tering.line lg through line. [3 must besufiiciientl-y h h, o adi S s end h a sac m m therein. The exact velocity of such gas will d-, 19 .1 11 largelyupon. the size and shape of the par-ticles o he ads m ve ed mw e lo iparticles of adsorptive medium musi from about 12 toahout 3.0 meshvsize, the velocity of the suspending. gas can range from. 10 to about'fet o r stoma e e abl f om e to bo t 20' ice-t P 4 seme- Th loei o thisle ase us stream hoi d be closel ateen-t ee to .lavoid-centrifugalseparationmf .the suspended particles .in the .cooling conduit fl 1-"and also to aigoidi settlinginv vertical linetB. llhe factors which.deter'minezthe exact-velocity of the gaseous suspendingagem inyline i2,conduit I l, and line I Buare.morefullydiscussed below.

Thisinvention also relates to a novel type of heat exchange, apparatusparticularly adapted. to beused in. the above-described process.Referring to'Figuregone embodimentof this heat exchange apparatusisshownasa coil generally designated bythenumeral'i'l. Coil Tiscomprisedzof a'conduit. 28 which is circular in cross-section andiscoiled abouta central. axis in such manner that thezraidiusofxcuryatureR-of coil is constant. The exactradius of curvature chosenwill depend upon the velocityv of? the gaseous suspension. flowingthrough the coil. Thatis, if the radius of coil Il'xlSlllOO small, anexcessive centrifugal force willbe developed by the flow offtheadsorbent suspension. through the coil so that the particles insuspensionin. the gas. will be thrown out v of suspension. andagainstthe outer walls of the 00115- duitld therebyclogging. the coil.On'the' other hand. theradiusotcurvature R shouldnot he so large.- as tomakethei cooling coil IT uneconomically large. Wehave found that, whenemploying the abovespecifiedvapor velocities; the radius of curvature, Rof coil llcan be as smallas 3. feet without clogging of. the coil bycentrifugalseparationoilthesuspended partices from the entrain inggas.The internal diameter of the conduit 2:8 )Vhi'ChfDIIIIlSiUhCOiL i l-canbe constantithroughout. theleng'th. of. coil H "In: such'case; thevelocity of.- the suspension of. adsorptive medium therethrough will.decrease as the temperature of thesuspensicrr is decreased. Hence, as apreferrerl featureof this invention, the diameter of conduit; 381 isvaried-"to "maintain the velocity of gaseous: suspension constant. Thatis, the square of the: diameter of conduit 231s maintained proportional'to the absolute temperature of the gasconssusrension. For example, if.the diamcter'of conduit 28 at. the inlet to coil IT is 3 inches and thetemperature, of. the gaseous suspension. is reduced trcm 500? E. to F.while flowing through. coil. til their the diameter of conduit 28 at theoutlet from coil ill should be about 2.3 inches. The; diameter of theportion oiv conduit 28 between theinl'et and: the'outlet to boil l7'ca'n'be decreased from 3. inches to 235' inches either in directproportion'to: the'lengthz of conduit nor in directproportion to thesquare root of the drop in absolute temperature of the" gaseoussuspension flowing through conduit 23'. As a novel feature 0t this,invention there is placed withirr'the conduit 23: forming. coil i'l aseries of small fins 3.9 which radiate inwardly into the conduit 28 fromthe inner. Mail-1 thereof as shown in Figure 33; which is. an enlarged"sectional View of a portion of the conduit 23 forming coil ll takenalong the longitudinal axis or thesaid'conduit. These fins are: furtherillustrated in Figure 4 Which'is across-sectional View on line 4-6 Asshown; the fins 29- are; surfaces which radiate inwardly toward thelongitudinal. axis of conduit 28 from the inner wall of conduit 28. Theradial center line 300i the fin- 29 isdisplaced outwardly from. thevertical diameter 33- of the conduit 28 in order thatthe center line oithe fin will correspond approximately with the point at which the majorportion of any adsorptive media tends to settle out in the coil. Theangular displacement of the centerline of the fin from the verticaldiameter uthe eil sseeveasedee eesin ris e-e T is angle A should besufiicient to permit the centerline of the fin to coincide with thepoint at which the entrained medium tends to settle out inthe coil. Thusthe separated medium will not settle out onto the bottom of conduit 28because of the centrifugal force exerted thereon and, neither will themedium settle out completely on the horizontal axis of conduit 28because of gravitational action on the separated particles of medium.Hence, the medium tends to settle out at a point between the horizontalaxis of the conduit and the bottom of the cross section. Therefore, thecenterline of fin 29 is coincident with this point of settling. Usuallythe fins will function properly to resuspend the settled media if theangle A of Figure 4 is between 30 and 50 degrees, preferably 45 degrees.The fin should be slanted downstream with the direction of flow. Onemeans of forming a fin is to form it as a segment of a parabola andinsert it into the circular conduit forming the coil so that the finslopes downstream and is displaced from the vertical diameter of theconduit. However, other forms of fins can be employed and the term finis used herein to designate any projection on the inside of a pipe orconduit which serves to resuspend any separated medium in the gas eouscarrier. Thus, as the gaseous suspension of adsorptive media flowsthrough the coil, any of the media which settles out onto the wall ofthe coil is scooped up by the fin and swept back into the center of theflowing gas stream where it is picked up again and conveyed along thelength of the coil. A plurality of fins 29 are usually employed alongthe length of cooling coil I! as shown in Figure 2. The exact number offins should be great enough to prevent any substantial settling of theadsorptive medium in the coil. Usually if the fins are spaced from 1 to3 feet apart, the adsorptive medium will be kept in suspension.

Figures 5 and 6 illustrate another embodiment of a cooling coilespecially adapted to be used in the process of this invention. Thisparticular embodiment can be substituted for coil I1. In the figure,conduit 32 corresponds to the conduit 28 of coil I! of Figure 2 andforms a passageway for the gaseous suspension of hot adsorptive medium.As shown, conduit 32 comprises a length of conduit which has been foldedor plaited into a series of S-shaped or undulated configurations, Thestraight portions of this conduit designated as 33 can extend for thewidth of the heat exchanger and terminate at their ends into a returnelbow 34. The radius of the return elbow is governed by the sameconsiderations as govern the radius of cooling coil [1 described above.The conduit 32 is rectangular in cross-section with the short side ofthe rectangle being disposed parallel with the length of the heatexchanger as shown in Figure 6 which is a cross-sectional view taken onthe line 66 in Figure 5. This particular rectangular cross-sectionalconfiguration of conduit 32 results in rapid cooling of the hotadsorptive material flowing therethrough since the distance throughwhich the heat must be transferred is small as compared with the radiusof a circular conduit of similar cross sectional area. Furthermore theturbulence of the suspension flowing through a rectangular section isgreater than that flowing through a circular section. Hence the rate ofheat transfer is greater for this section than for a circular section.The cross-sectional area of conduit 32 can be varied with the drop intemperature of the gaseous suspension flowing therethrough as explainedabove with reference to coil [1. Fins 35 are disposed along the lengthof conduit 32 similar to those disposed in coil l1.

These fins are situated along the bottom side of conduit 32 and therebyserve to elevate any separated adsorptive media back into the gas streamfor resuspension therein. Since the adsorptive media which may separatein the elbow 34 will tend to fall back by gravity into the gas stream asit emerges from the elbow and thereby become resuspended in the gas, itis apparent that fins need not be located near the point where thegaseous suspension emerges from the return elbows. Hence, the majorityof the fins 35 in conduit 32 should be located near the point where thestraight portion 33 of the conduit joins the return elbow 34. Theconduit 32 is surrounded by a vessel 36 constructed with baffles 31extending beline 38 will flow substantially counter-current to the flowof gaseous suspension through conduit 32. The heated cooling mediaemerges from vessel 36 through line 39.

Variation and modification are possible within the scope of thisinvention the essence of which is that the efficiency of a hypersorptionprocess can be improved by cooling the hot freshly stripped adsorptivemedium while it is suspended in an upwardly flowing carrier gas wherebythe rate of heat transfer from the hot medium is increased without undueattrition of the adsorbent medium particles and without any substantialsettling of the said particles from the gaseous carrier and that a novelheat exchange apparatus especially adapted to be employed in theforegoing process has been provided.

I claim:

1. A heat exchange apparatus adapted to cool a gaseous suspension of agranular solid comprising a vessel having disposed therein a conduit ofrectangular cross-section having a plurality of plaits along itslongitudinal axis and with the long side of said rectangularcross-section of said con-'- duit perpendicular to a plane through thelongitudinal axis of said plaited conduit, said plaited conduit having across-sectional area which decreases along the length of said conduit indirect proportion to the decrease in the absolute temperature of saidsuspension flowing therethrough whereby the velocity of said suspensionis maintained substantially constant throughout the length of saidconduit, the radius of curvature of the upturning sections of saidplaits being large enough to prevent particles from being thrown out ofsaid suspension, said plaited conduit having disposed therein aplurality of fins along its inner bottom surface, each of said finscomprisin a rectangle fastened along three of its sides to three sidesof the said conduit and inclined in the direction of flow through saidconduit, the majority of said fins being positioned near the point wherea horizontal portion of said plait joins an upturning section of saidplait, baflles disposed in said vessel to extend between the folds ofeach plait of said conduit whereby the coolant flowing through saidvessel passes counter-currently to the flow of gaseous suspensionthrough said conduit.

2. A heat exchange apparatus adapted to cool a gaseous suspension of agranular solid comprising a vessel having disposed therein a conduit ofrcc tangular cross-section having a plurality of plaits along itslongitudinal axis and with the long side of said rectangularcross-section of said conduit perpendicular to a plane through thelongitudinal axis of said plaited conduit, the upturning sections ofsaid plaits having a radius of curvature large enough to preventparticles from being thrown out of suspension, said plaited conduithaving disposed therein a plurality of fins along its inner bottomsurface, each of said fins comprising a rectangle fastened along threeof its sides to three sides of the said conduit and inclined in thedirection of flow through said conduit, the majority of said finslocated in the straight portion of said plait near where said straightportion joins the upturning portion, baffies disposed in said vessel toextend between the folds of each plait of said conduit whereby thecoolant fiowing through said vessel passes counter-currently to the flowof gaseous suspension through said conduit.

3. A heat exchange apparatus adapted to cool a gaseous suspension of agranular solid comprising a vessel having disposed therein a conduit ofrectangular cross-section and having a plurality of convolutions alongits longitudinal axis and with the long side of said rectangularcrosssection of said conduit perpendicular to a plane through thelongitudinal axis of said convoluted conduit, a straight section of saidconduit connecting two said convolutions which have a radius ofcurvature large enough to prevent particles from being thrown out ofsuspension, said convoluted conduit having disposed therein a pluralityof fins along its inner bottom surface, each of said fins comprising arectangle fastened to the bottom of said conduit and inclined in thedirection of flow through said conduit, the majority of said fins beinglocated near the juncture of a straight portion of said conduit with anupturning convoluted section of said conduit baflies disposed in saidvessel to extend between the folds of each convolution of said conduitwhereby the coolant flowing through said vessel passes countercurrentlyto the flow of gaseous suspension through said conduit.

4. A heat exchange apparatus adapted to cool a gaseous suspension of agranular solid comprising a convoluted conduit of rectangularcrosssection and having the long side of said rectangular cross-sectionof said conduit perpendicular to a plane through the longitudinal axisof said convoluted conduit, the radius of curvature of a section joiningtwo horizontal sections of said convolutions being large enough toprevent particles from being thrown out of suspension, said convolutedconduit having disposed therein a plurality of fins along its innerbottom surface, each of said fins comprising a rectangle fastened to thesaid conduit, the majority of said fins being located near eachupturning section of said convoluted conduit and inclined in thedirection of flow through said conduit.

5. A heat exchange apparatus adapted to cool a gaseous suspension of agranular solid comprising a conduit plaited along its longitudinal axis,said plaited conduit having disposed therein a plurality of finsinclined in the direction of flow and positioned along its inner bottomsurface, the majority of said fins being located near the point wherethe straight portions of said plait join the upturning portions, wherebysaid granular solid is maintained as a suspension in said gas.

6. The heat exchange apparatus of claim 5. wherein said plaits have aradius of curvature of at least 3 feet.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 565,866 Winkel Aug. 11, 1896 837,582 Ordway Dec. 4, 1906849,579 Siebel Apr. 9, 1907 1,280,656 Buhr Oct. 8, 1918 1,363,955Conover Dec. 28, 1920 1,531,974 Reiser Mar, 31, 1925 1,698,789 GillicanJan. 15, 1929 1,785,159 Ullman Dec. 16, 1930 1,825,707 Wagner Oct. 6,1931 2,348,009 Johnson May 2, 1944 2,449,822 Schibbye Sept. 21, 19482,476,472 Arnold et al July 19, 1949 2,520,747 Van Den Broek Aug. 29, 0

FOREIGN PATENTS Number Country Date 345,279 Great Britain Mar. 17, 1931

